It is often necessary to replace existing underground pipes forming part, for example, of drinking water, sewage or gas mains. A pipe has to be replaced for example when an existing pipe is in a poor state of repair or when, further to an increase in the load, the capacity of the existing pipe is no longer sufficient.
A first, and oldest, manner of replacing the pipes consists in effecting a complete excavation, which is expensive and considerably detrimental to the environment, particularly in urban areas, insofar as the roadway and/or pavement of a street must be destroyed.
Another manner of replacing an existing pipe, developed more recently on an industrial scale, consists, in order to avoid excavation, in introducing a new pipe inside the old one. Of course, this means that the new pipe must present an outer diameter smaller than the inner diameter of the old pipe, hence a reduction in the section of passage, which prevents this technique from being employed if the capacity of transport is to be maintained or increased, unless the pressure of the fluid conveyed is modified.
Another manner of replacing a pipe consists in fragmenting the pipe in situ by means of a special tool, in pushing the fragments radially towards the outside, then in introducing a new tube in the space thus created. This technique is described in particular in document EP-A2-0094694 which relates to a process for inserting a new pipe in place of an old one after splitting the latter, and in document EP-B1-0053480 which relates to particular devices for employing the process mentioned above.
In the splitting technique described in the documents cited above, a percussion device acts on the fracturing tool brought into contact with the existing pipe in order to cause fragmentation thereof. Use of a percussion tool provokes vibrations which may disturb the immediate environment of the pipe to be replaced, which constitutes a nuisance particularly when several pipes of different nature lie underground in the vicinity of one another.
Moreover, the splitting technique can only be used where the pipe is sufficiently fragile and made of a material such as grey pig-iron for example, which is easily broken. If, as is generally the case, certain sections of pipe have already been repaired and include different, more resistant and non-brittle materials, such as ductile cast iron or steel, the fracturation tool is blocked on these non-brittle sections which are generally not indicated on the plans. The tool may itself be damaged and in any case it is then necessary to return to a traditional method of excavation to disengage the tool and proceed with the fracturation or removal of the non-brittle section. The fact of interrupting here and there the advance of the fracturation tool and of proceeding with a conventional excavation in the ground, slows down the whole process and thus constitutes a loss of time and money.
Furthermore, the splitting of a pipe into a multiplicity of fragments capable of obstructing the passage makes it necessary to effect the fracturation, spreading of the fragments of the split pipe and positioning of the new pipe, in one single operation. This may present drawbacks if the new pipe to be laid is not immediately available. In fact, in that case, it is not possible to commence destruction of the existing pipe and to effect laying of the new pipe in a second step.
Document U.S. Pat. No. 3,181,302 discloses an apparatus for replacing a substantially horizontal underground pipe. The apparatus comprises a cutting tool constituted by a certain number of cutting discs mounted so as to be able to rotate on a supporting bar, the cutting tool being provided to be towed in the pipe by means of a winch cable with the result that the discs progressively split the pipe into two parts in the longitudinal direction.
The rear end of the cutting tool is connected to a conical device for spreading the two halves of cut pipe apart and a new pipe, connected to the spreader device, is engaged in the space previously occupied by the existing pipe.
This technique employs heavy, sophisticated and expensive equipment and requires a very high-power traction element since it must provoke mechanical cutting with the aid of towed cutting elements, whilst also towing the spreader element and the new pipe. The apparatus therefore often act jerkily, which hinders advance. Furthermore, in the case of brittle materials, mechanical cutting produces fragments which may block the cutting mechanism.
Various industrial metal cutting processes are also known, of which certain, such as oxygen-cutting, plasma cutting, laser cutting, fusion drilling, cutting by torch employing powdered iron, enable the metal to be heated beyond its melting point. Various industrial cutting processes are also known, based on the localized projection of a fluid under pressure, the latter being homogeneous, for example water, or non-homogeneous, for example water containing an abrasive agent such as inorganic particles. However, these various processes have not yet been applied to remote-controlled underground works for replacing underground pipes.
It is an object of the present invention to overcome the drawbacks set forth hereinabove and to effect in situ, continuously and without jerks, the cutting of an underground pipe, without it being necessary to proceed with excavations.
It is a further object of the invention to cut an existing pipe, limiting the risks of blocking the cutting device.
The invention also aims at allowing a new pipe to be laid, whose diameter is substantially equal to or greater than that of the existing pipe, either during an operation combined with that of the cutting of the existing pipe or during a subsequent step distinct from the cutting operation, as desired, and without it being necessary to proceed with the removal of the existing pipe.
It is a further object of the invention to allow a pipe to be replaced with the aid of a device involving only moderate efforts of traction, and to enable the operational parameters of the cutting device to be easily adjusted and if necessary automatically adapted as a function of the characteristics of the existing pipe.